A typical LCD has the advantages of portability, low power consumption, and low radiation. Therefore, the LCD has been widely used in various portable information products, such as notebooks, personal digital assistants, video cameras, and the like.
FIG. 5 is a block diagram of a typical LCD. The LCD 100 includes a power supply circuit 11, a scaler 15, an LCD panel 16, an inverter 17, and a backlight module 18. The power supply circuit 11 is used for transforming external alternating current (AC) voltages into direct current (DC) voltages. The DC voltages are transmitted to the LCD panel 16, the scaler 15, and the inverter 17, respectively. The scaler 15 is used for receiving external video signals and generating control signals. The video signals are transmitted to the LCD panel 16, and the control signals are transmitted to the LCD panel 16, the power supply circuit 11, and the inverter 17, respectively. The inverter 17 is used for transforming the DC voltages into high-frequency AC voltages, and the high-frequency AC voltages are used for driving lamps (not shown) of the backlight module 18 to light up.
Shutting down the LCD 100 should be done by pressing a mechanical switch (not shown) located on a housing (not shown) of the LCD 100. When the mechanical switch is pressed, the mechanical switch transmits a control signal to the scaler 15. Firstly, the scaler 15 transmits a first shutting down signal to shut down the inverter 17. Then, the scaler 15 stops transmitting the video signals to the LCD panel 16. Finally, the scaler 15 transmits a second shutting down signal to shut down the power supply circuit 11. The entire operation above is called “DC off.”
When the mechanical switch is not pressed and the external AC voltage suddenly drops to zero, the power supply circuit 11, the inverter 17, and the scaler 15 are shut down at the same time, as shown in FIG. 6. This is called “AC off.” If AC off occurs many times, electrical elements of the LCD 100 are liable to be damaged or even destroyed.
What is needed, therefore, is an LCD that can overcome the above-described deficiencies.